1. Field
This disclosure relates generally to semiconductors, and more specifically, to storage circuits that are cache memories for processors.
2. Related Art
Lower power consumption continues to have importance in data processing systems, due, for example, to widespread use of portable and handheld applications. Most data processing systems today use a smaller, faster, and more efficient memory, referred to as a cache, located on the integrated circuit to reduce the number of accesses to memory (such as main memory or other internal or external memories). It is well known that accesses to cache generally consume less power and result in reduced latencies as compared to accesses to other internal or external memories. Therefore, it is desirable to store those items which will subsequently be requested again in the faster, more efficient cache in order to reduce power and increase performance.
Cache pollution occurs both when information which has a lower degree of reuse replaces information which would have a higher degree of reuse if it were still present in the cache and when data is intentionally redundantly stored in the cache for error detection purposes. For the former, items with a higher degree of reuse should remain in the cache because it is more likely that they will be requested again (e.g. requested again multiple times). For example, some information has shorter lifetimes as compared to other information, and cache pollution by this shorter lifetime information can increase power consumption and reduce performance of the cache since it is likely that the higher lifetime information will have to be refetched from the slower, less efficient internal or external memory after having been replaced by the shorter lifetime information. However, it is still desirable to allow the information with shorter lifetimes to benefit from reuse within a cache. Implementing the redundant storage of data in a cache causes the effective working capacity of the cache to be reduced and thus results in a lower performing system.